This invention relates to an electrophotographic photoreceptor and more particularly, to an electrophotographic photoreceptor which comprises a conductive support and a light-sensitive layer, provided thereon, containing a bis-azo pigment.
There have, heretofore, been known and widely studied and practically used inorganic photoconductive materials such as selenium, cadmium sulfide, zinc oxide, silicon, etc. for electrophotographic photoreceptors. In recent years, in addition to the inorganic photoconductive materials, organic photoconductive materials have also been actively studied and some of them have been practically used in electrophotographic photoreceptors.
In general, inorganic materials are not necessarily satisfactory, for example, selenium photoconductive material has problems in heat stability, deterioration of characteristics due to crystallization and difficulties in production and in the case of cadmium sulfide there are problems in moisture resistance, endurance and disposal of industrial waste. On the other hand, organic materials have advantages such as good film forming property, superior flexibility, lightness in weight, good transparency and easiness in design of photoreceptors for wide wavelength range by employing suitable sensitizing method. Thus, much attention has been attracted on practical use thereof.
The electrophotographic photoreceptors are, generally, required to have the following basic properties: (1) They can be charged highly with corona discharge in the dark. (2) Leakage of charges in the dark (dard decay) is a little. (3) Dissipation of charges upon exposure to light (light decay) takes place rapidly. (4) Residual charge after exposure to light is a little.
Photoconductive polymers such as polyvinylcarbazoles, etc. have been extensively studied as organic photoconductive materials. However, these are not necessarily satisfactory in film formability, flexibility and adhesion and besides they do not sufficiently possess the above enumerated basic properties required as photoreceptors.
On the other hand, organic low-molecular photoconductive compounds can provide photoreceptors excellent in mechanical properties such as film forming ability, flexibility, adhesion, etc. by proper selection of binders used for preparation of photoreceptors, but it is difficult to find compounds capable of retaining high sensitivity.
In an attempt to improve these problems, there has been developed an organic photoreceptor of high sensitivity in which the carrier generating function and the carrier transport function are respectively borne by different substances, such a type of photoreceptors called functionally separated type have the advantages in that the materials suitable for the respective functions can be selected from a wide range and photoreceptors having optional properties can be easily produced.
There have been proposed various photoreceptors of the functionally separated type which contain organic dyes or organic pigments as a carrier generating substance. For example, photoreceptors which contain dis-azo pigments or tris-azo pigments are disclosed in Japanese Patent Unexamined Publication (Kokai) Nos. 22834/79, 46237/81, 196241/82, etc. Sensitivity of these photoreceptors is not necessarily sufficient for practical use and further, they do not satisfy various requirements for electrophotographic process. Thus, further increase of sensitivity is desired.
In further recent years, as the light sources to be used for photoreceptors, there have been proposed laser beams of relatively shorter wavelength beams such as argon laser beams, He-Ne laser beam, etc. and further those of longer wavelength such as semiconductor laser beam. Thus, it has been earnestly desired to develop photoreceptors of high sensitivity which can use the wavelength of semiconductor laser beam (about 780 nm).